In the discussion of the background that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicants expressly reserve the right to demonstrate that such structures and/or methods do not qualify as prior art.
Effect pigments are typically composed of a plurality of particulate substrates coated with one or more reflecting/transmitting layers. Typically, effect pigments are substrates, such as natural mica or glass, that have been coated with a metal oxide layer. If a colorless metal oxide is used to coat the particulate substrate, then the effect pigment can exhibit a pearl-like luster as a result of the reflection and refraction of light. Further, effect pigments can also exhibit interference color effects. If colored metal oxides are used, then the observed effects depend on reflection, refraction, and absorption.
Effect pigments are known as pearlescent pigments or nacreous pigments, and can be used to impart a pearlescent luster, metallic luster, and/or multi-color effect approaching iridescence, to a material. For example, an effect pigment can be incorporated into a cosmetic or a personal care composition to provide color, iridescence, luster, and/or a pleasing tactile property.
Effect pigments have been produced by depositing iron oxide directly onto substrates, such as mica. However, the deposition of iron oxide using wet techniques, such as the aqueous deposition of FeCl3 to form an iron oxide coating may result in disadvantageous levels of toxic metals, and other impurities. Further, such wet deposition methods typically require calcination of the effect pigments at temperatures in excess of 500° C. When TiO2 is present with Fe2O3, the high calcination temperature can result in the formation of iron titanate species. Effect pigments have been produced using chemical vapor deposition (CVD) techniques to deposit iron oxide onto substrates. However, the purity of these pigments and the absence of iron titanante formation has not been previously explored or established.
There is an on-going need in the art for iron oxide containing effect pigments having improved properties.